Underlayers, such as organic planarizing layers or spin-on carbon layers, play a very important role in various integration schemes of chip manufacturing. One function of organic planarizing layers is to fill in pre-existing patterns on substrates, such as previously patterned vias, to enable lithographic patterning of the next level. More importantly, organic planarizing layer resistance to reactive ion etch (RIE) processes used to etch silicon-containing materials is essential for the successful pattern transfer from resists into the substrate.
Typically, a pattern is first transferred into the organic planarizing layer through a two-step RIE sequence, followed by the transfer into the substrate by a fluorine-containing RIE step that leaves the organic planarizing layer pattern mainly intact (FIG. 1). However, when the line/space patterns are scaled down to line widths below 35 nanometers (nm) (of course the actual onset depends on the organic planarizing layer material, the RIE tool and RIE chemistry used and the aspect ratio), it was found that this last RIE step induces severe pattern deformation (“wiggling”) of the organic planarizing layer material, which ultimately prevents the successful pattern transfer into the substrate. For examples of wiggling of the organic planarizing layer material see M. Glodde et al., “Systematic Studies on Reactive Ion Etch-Induced Deformations of Organic Underlayers,” Proc. SPIE, 7972 797216 (2011) (hereinafter “Glodde”), the contents of which are incorporated by reference herein.
It was previously found that employing a high temperature post-apply bake at 350 degrees Celsius (° C.) or above, helps improve performance. However, a high temperature post-apply bake step is not always possible. And in fact, this post-apply bake sometimes even has a negative impact on other material properties. For example, it was found that the adhesion of hydrogen silsesquioxane (HSQ) patterns generated through electron beam lithography to the organic planarizing layer is much better when the organic planarizing layer is baked at lower temperatures. This is a general trend, as HSQ adhesion is thought to depend on the presence of polymer-bound hydroxyl groups that disappear during high temperature processing due to cross-linking.
Another example are materials that have thermally unstable yet important additional components blended with, or bound to, the polymer backbone of the organic planarizing layer material, such as near infrared (NIR) dyes that are only thermally stable at temperatures up to from about 200° C. to about 220° C. See, for example, U.S. Application Publication Number 2011/0042771 filed by Huang et al., entitled “Near-Infrared Absorbing Film Compositions” and U.S. Application Publication Number 2011/0042653 filed by M. Glodde et al., entitled “Near-Infrared Absorbing Film Compositions,” the contents of each of which are incorporated by reference herein. In these cases, the second post-apply bake at 350° C. or above would lead to severe degradation of beneficial material properties, eliminating this high temperature baking step as a viable option. Further, a high temperature post-apply bake can also change the optical constants, and thus the light absorbing/optical properties of the organic planarizing layer, in which case the material can no longer be used as a bottom anti-reflective coating (BARC).
In a previous approach to improve the pattern transfer, described in U.S. Patent Application Publication Number 2009/0174036 filed by Fuller et al., entitled “Plasma Curing of Patterning Materials for Aggressively Scaled Features,” (hereinafter “U.S. Patent Application Publication Number 2009/0174036”), the contents of which are incorporated by reference herein, a UVCure plasma treatment in the RIE tool is inserted before and after the organic planarizing layer open etch step. However, it was shown that the results of this process are very sensitive to how the wafers are handled. For example, if the wafers are simply removed from the vacuum chamber for top-down scanning electron micrograph (SEM) inspection after the UVCure plasma treatment, this level of handling causes the lines to bend severely. This sensitivity could be part of the reason why this plasma curing method does not seem to work well when actually implemented in practice.
Thus, improved techniques for pattern transfer into inorganic substrates wherein pattern deformation of the organic planarizing layer material is minimized, or eliminated, would be desirable.